1. Measuring Pavement Thickness Nondestructively using Pulse Induction Technology Current Agency Practices TRB Session 1400 Quality Assurance in Construction and Smart Technology
Jagan Gudimettla, P.E.
ATI Inc (Consultant to FHWA)
Office of Preconstruction, Construction, and Pavements

2. Acknowledgments Todd Hanson (Iowa DOT) Kevin Jones (Iowa DOT)
Chad Hayes (Wisconsin DOT)
Robert Golish (Minnesota DOT)
Gregory Johnson (Minnesota DOT)
Richard Howell (Minnesota DOT)

3. Outline Pavement Thickness Pulse Induction Method
State DOTs Experiences
Concrete Pavement Thickness
Asphalt Pavement Thickness
Current State of Practice
Summary

4. Pavement Thickness Significantly influences the life of pavement
Important quality assurance activity for agencies
Methods to measure pavement thickness
Probing (Quality Control)
Coring (Most Prevalent) (Acceptance)
Non-destructive methods
Impact Echo
Ground Penetrating Radar (GPR)
Ultrasonic Pulse Echo (MIRA)
Pulse Induction Technology (MIT Scan T2/MIT Scan T3)

5. Traditional Tests Destructive Expensive Time Consuming - core
- inspect
- handle
- measure
- patch core holes
Probing
(Quality Control)
Coring
(Acceptance)

6. Pulse Induction Technology
Step 2
Step 3
Step 1
Find the target and
measure thickness
Place the target
Pave over it
Quality Control and Agency Acceptance
AASHTO Test Method (AASHTO T )
ASTM Test Method in the works

7. Pulse Induction Technology
Advantages
Easy to use
High accuracy
Non-destructive
Almost real time
Rapid measurement
Significant cost savings
Data storage (text files)
Independent of the base material
Calibration with core not required

8. Pulse Induction Technology
Accuracy
FHWA Mobile Concrete Trailer (MCT) Data

9. Pulse Induction Technology
Limitations
Only for new construction
Measurements 2-3 feet away from steel
GPS enabled
Hardware enhancements
Software enhancements
MIT Scan T2
MIT Scan T3

10. Pulse Induction Technology
Metal Targets or Reflectors
4.7"
2.7"
4.7"
11.8"
11.8"
14“
Asphalt
Concrete

11. Field Implementation FHWA Mobile Concrete Trailer (MCT) Since 2007
Field Visits
Equipment Loan

12. Iowa DOT Timeline Technology introduced (Spring 2008)
Equipment Loan (Fall 2008)
Evaluated the technology on two projects (2009)
Trial Specification – four projects (2010)
Full Specification (2011)
Purchased several devices for each of their 6 districts
Worked with MCT staff to develop an AASHTO Test Method ( )

13. Question
If the MIT Scan T2 needs metal targets… Do we lose the element of random sampling (surprise)?

14. Iowa DOT
Procedure
Place targets every 200 ft randomly 4 or 8 foot right or left of centerline (avoid steel)
One nail hole in the middle of the target

15. Iowa DOT
Procedure
Random number (~50 to 65%) of targets are randomly selected
The MIT Scan T2/T3 is used to find the location of the target
Test by slow walking speed.
Test 3 times. Results need to be within 3 mm, if not, 2 additional readings are taken

16. Iowa DOT Old Spec New Spec Core 1 random location every 2000 sq. yds.
Four metal targets every ~2000 sq. yds.
Two MIT Scan measurements every ~2000 sq. yds.

17. Iowa DOT Issues with Granular Subbase 9 point measurement
Core off target, core on target
9 point measurement
Concrete migrates into the aggregate base
Core test results are slightly thicker

18. Iowa DOT Thickness Incentive Thickness index =
(Average Thickness – Std Dev.) – Design Thickness
Unit price adjusted up to 103% - or less
Correction for type of base
Type of Base, Subbase, Subgrade just below the concrete
Adjustment to Design Thickness for Incentive Calculation
Natural Subgrade or Soil Aggregate Subbase
Design Thickness
HMA Base, PCC Base, or Asphalt or
Cement treated Base
Modified Subbase or Special Backfill
Design Thickness minus 0.25 inches
Granular Subbase
Design Thickness minus 0.35 inches

19. Iowa DOT Currently have 12 MIT Scan T2 and 4 MIT Scan T3
Agency tests verification and Materials checks Independent Assurance with different gage

20. Minnesota DOT Timeline Since 2013
Dowel baskets and tie steel
Evaluated for thickness in 2015 and 2016: 9 pilot projects
Select projects in 2017 and 2018
Contractor request for using the T2, no cost supplemental
Starting in 2019 (Special Provision) all projects
Concrete overlay of an existing asphalt pavement
Concrete placed directly on the grade
Not used on UBOL
Due to steel in the existing concrete

21. Minnesota DOT Frequency of Testing Prior to 2014
Coring frequency was 1 per 1000 lineal ft per lane
2014 to current (reduced coring and implemented more probing)
1 probe per 1000 lineal ft per lane
1 verification core per 4 probes
1 random core per 4000 lineal ft per lane
2019 and beyond (Special Provision)
1 scan per 1000 lineal ft per lane
1 verification core per 8 scans
1 random core per 8000 lineal ft per lane
8 cores / 8000 l ft
4 cores / 8000 l ft
2 cores / 8000 l ft
Cores and scans will be used to determine final average thickness

22. Wisconsin DOT Timeline Started using Thickness for Acceptance
2017
Ownership
Paving Contractors

23. Wisconsin DOT Procedure 250 ft basic units (for each lane)
Two plates in each unit by contractor
Longitudinal and transverse locations randomly determined
Within 3 feet from steel or within 4 feet from a joint
Anchor plates using 16D common nail

24. Wisconsin DOT
Procedure
The department will measure thickness at one random location in each unit
If the initial measurement falls within the 80 to 50 percent pay range, the department will measure at the second plate in that unit and average the results to determine pay adjustments

25. Wisconsin DOT Thickness Penalty
Pavement thinner than plan thickness by
Percent of the Contract Unit Price
> 0.25 in but ≤ 0.5 inch 80
> 0.5 in but ≤ 0.75 inch 60
> 0.75 in but ≤ 1 inch 50
> 1 inch
unacceptable
The department adjusts pay based on the average of 2 measurements per unit

26. What about Asphalt Pavements?
Tonnage (asphalt) versus SqYards (concrete)
Cores for density purposes (asphalt)
Minnesota DOT Experience
West Central district uses a pay item of square yard inch (SYI) for asphalt
Personnel Issue
Weight tickets - Fewer agency folks in the field
Additional cores are taken (above the normal density cores) to verify pavement thickness

27. Asphalt Pavements Minnesota DOT Experience
Procedure
Targets placement
Immediately prior to paving
Discs placed on the base
Invisible after the first lift (randomness)
4.7” plates, secured with one nail
Number of plates based on the total tonnage
Vary based on pavement thickness
Graduated deduction if paved too thin

28. State of Practice Full-Fledged Implementation Iowa DOT Wisconsin DOT
Minnesota DOT
West Virginia DOT
Illinois Tollway
Alabama DOT
Nevada DOT
Pennsylvania DOT
Certain districts

29. Field trials already performed or underway
Planned Activities
Implementing in 2019
Washington State DOT
North Dakota DOT
Considering implementing in 2019 or beyond
Delaware DOT
Florida DOT
Indiana DOT
North Carolina DOT
Arizona DOT
Field trials already performed or underway

30. Contractors Perspective
Need not wait until the cores are cut for payment
Cutting fewer or no cores
In case of disputes, core is taken over the metal plate
The scanner has been shown to be accurate.  

31. Summary Based on the State’s Data
Excellent correlation to core test results
Repeatable between operators and equipment
Can work for both concrete and asphalt pavements
Proven technology for Quality Control and Agency Acceptance
Major Benefits
Better statistical data (agency)
Almost real-time testing (contractor)
Cost, time, personnel (agency and contractor)

32. Questions ???
Contact info: